// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;

namespace Microsoft.Extensions.Diagnostics.HealthChecks
{
    /// <summary>
    /// Represents the result of executing a group of <see cref="IHealthCheck"/> instances.
    /// </summary>
    public sealed class HealthReport
    {
        /// <summary>
        /// Create a new <see cref="HealthReport"/> from the specified results.
        /// </summary>
        /// <param name="entries">A <see cref="IReadOnlyDictionary{TKey, T}"/> containing the results from each health check.</param>
        /// <param name="totalDuration">A value indicating the time the health check service took to execute.</param>
        public HealthReport(IReadOnlyDictionary<string, HealthReportEntry> entries, TimeSpan totalDuration)
            : this(
                entries,
                CalculateAggregateStatus(entries?.Values ?? throw new ArgumentNullException(nameof(entries))),
                totalDuration)
        {
        }

        /// <summary>
        /// Create a new <see cref="HealthReport"/> from the specified results.
        /// </summary>
        /// <param name="entries">A <see cref="IReadOnlyDictionary{TKey, T}"/> containing the results from each health check.</param>
        /// <param name="status">A <see cref="HealthStatus"/> representing the aggregate status of all the health checks.</param>
        /// <param name="totalDuration">A value indicating the time the health check service took to execute.</param>
        public HealthReport(IReadOnlyDictionary<string, HealthReportEntry> entries, HealthStatus status, TimeSpan totalDuration)
        {
            Entries = entries;
            Status = status;
            TotalDuration = totalDuration;
        }

        /// <summary>
        /// A <see cref="IReadOnlyDictionary{TKey, T}"/> containing the results from each health check.
        /// </summary>
        /// <remarks>
        /// The keys in this dictionary map the name of each executed health check to a <see cref="HealthReportEntry"/> for the
        /// result data returned from the corresponding health check.
        /// </remarks>
        public IReadOnlyDictionary<string, HealthReportEntry> Entries { get; }

        /// <summary>
        /// Gets a <see cref="HealthStatus"/> representing the aggregate status of all the health checks. The value of <see cref="Status"/>
        /// will be the most severe status reported by a health check. If no checks were executed, the value is always <see cref="HealthStatus.Healthy"/>.
        /// </summary>
        public HealthStatus Status { get; }

        /// <summary>
        /// Gets the time the health check service took to execute.
        /// </summary>
        public TimeSpan TotalDuration { get; }

        private static HealthStatus CalculateAggregateStatus(IEnumerable<HealthReportEntry> entries)
        {
            // This is basically a Min() check, but we know the possible range, so we don't need to walk the whole list
            var currentValue = HealthStatus.Healthy;
            foreach (var entry in entries)
            {
                if (currentValue > entry.Status)
                {
                    currentValue = entry.Status;
                }

                if (currentValue == HealthStatus.Unhealthy)
                {
                    // Game over, man! Game over!
                    // (We hit the worst possible status, so there's no need to keep iterating)
                    return currentValue;
                }
            }

            return currentValue;
        }
    }
}
